In boilers that use petroleum fuel as fuel like in electric power plants, boiler sludge is deposited on the bottom of a boiler and dust collectors catch boiler ash. In the boiler sludge and boiler ash, heavy metals such as Ni and V are condensed as oxides. In ammonium metavanadate which is obtained by performing wet alkali treatment with the boiler ash, a heavy metal of V is condensed as an oxide.
In the field of oil refinery, gas processing industry and others, desufurization catalyst is spent in the refinery process. Once spent in this process, the desufurization catalyst also contains, as oxides, heavy metals of Ni, Mo, and V in the form of condensation. It is desired to recover these oxides, which are Ni, Mo and V, in the form of metal, which promotes more effective use of waste materials.
As one of techniques for recovering valuable metals from those V, Mo and Ni containing materials, the inventors have proposed a method of recovering a valuable metal, the method including a roasting step of roasting a V, Mo and Ni containing material; a step of charging a heating furnace with the V, Mo and Ni containing material, a reducing agent and flux and heating them for reduction thereby to produce a V-containing slag and a Fe—Mo—Ni base alloy; and a step of charging a reducing agent for the V-containing slag to produce an Fe—V base alloy and a CaO—Al2O3 slag (see Patent document 1, claim 1).
In this valuable metal recovering method disclosed in the patent document 1, the C and S components in the V, Mo and Ni containing material are first removed as oxides in the roasting step, and then the reducing agent is used to reduce the V, Mo and Ni containing material to produce a Fe—Mo—Ni base alloy. This reduction is followed by desulfurization and decarbonization of the Fe—Mo—Ni base alloy. The desulfurization and decarbonization are in compliance with the standards, applied in the field of steel handling Fe—Mo—Ni base alloy, which requires the sulfur component to be lowered.    Patent document 1: Japanese Patent Laid-open (unexamined) Publication No. 2004-285473